Communicating via the usb-to-ttl-serial adapter, Section 6 – Pololu USB AVR User Manual
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6. Communicating via the USB-to-TTL-Serial Adapter
One bonus feature of the Pololu USB AVR programmer is the USB-to-TTL-serial adapter, which can be used for
connecting microcontroller projects to a personal computer. The programmer’s drivers make the USB-to-TTL-serial
adapter look like a standard serial port to the operating system, allowing you to use existing terminal programs
and software that are designed to use serial ports. This feature is similar to the
product, except the programmer has fewer control lines available and transmits at
5 V.
The TX and RX lines of the programmer are used to send asynchronous serial communication. When the programmer
receives a byte from the computer via USB, it will transmit that byte on the TX line. When the programmer receives
a byte on the RX input line, it will send that byte back to the computer via USB.
The bytes are sent and received eight bits at a time, with no parity and one stop bit. This coding is sometimes
abbreviated 8N1. The bits must be non-inverted, meaning that a zero is sent as low voltage, and a one is sent as high
voltage. All devices involved in asynchronous serial communication need to agree ahead of time on the duration of
one bit (the baud rate), so all devices must be independently configured to run at the same baud rate before they
will be able to communicate with each other. The USB AVR programmer supports all integer baud rates from 110 to
115200 bits per second. The following figure is an example of an 8N1 TTL serial byte:
To use the USB-to-TTL-serial adapter, you must first determine what port name the operating system has assigned it.
To determine the port name in Microsoft Windows, open the Device Manager, expand the “Ports (COM & LPT)” list,
and look for the “Pololu USB AVR Programmer TTL Serial Port” entry. The port name will be at the end of this line
in parentheses (e.g. “COM4”). In Windows, a given device will always be associated with the same port unless you
manually change its port assignment (see
Pololu USB AVR Programmer User's Guide
© 2001–2014 Pololu Corporation
6. Communicating via the USB-to-TTL-Serial Adapter
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